blob: a5b802a1221272402b344d75ccf94bcff4b69b38 [file] [log] [blame]
Greg Kroah-Hartmanb2441312017-11-01 15:07:57 +01001// SPDX-License-Identifier: GPL-2.0
Linus Torvalds1da177e2005-04-16 15:20:36 -07002#include <linux/kernel.h>
3#include <linux/errno.h>
4#include <linux/sched.h>
5#include <linux/user.h>
Roland McGrath4c79a2d2008-01-30 13:31:52 +01006#include <linux/regset.h>
Al Viro2cf09662013-01-21 15:25:54 -05007#include <linux/syscalls.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07008
Linus Torvalds7c0f6ba2016-12-24 11:46:01 -08009#include <linux/uaccess.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070010#include <asm/desc.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070011#include <asm/ldt.h>
12#include <asm/processor.h>
13#include <asm/proto.h>
14
Roland McGrath4c79a2d2008-01-30 13:31:52 +010015#include "tls.h"
16
Linus Torvalds1da177e2005-04-16 15:20:36 -070017/*
18 * sys_alloc_thread_area: get a yet unused TLS descriptor index.
19 */
20static int get_free_idx(void)
21{
22 struct thread_struct *t = &current->thread;
23 int idx;
24
25 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
Roland McGrathefd1ca52008-01-30 13:30:46 +010026 if (desc_empty(&t->tls_array[idx]))
Linus Torvalds1da177e2005-04-16 15:20:36 -070027 return idx + GDT_ENTRY_TLS_MIN;
28 return -ESRCH;
29}
30
Andy Lutomirski41bdc782014-12-04 16:48:16 -080031static bool tls_desc_okay(const struct user_desc *info)
32{
Andy Lutomirski3669ef92015-01-22 11:27:59 -080033 /*
34 * For historical reasons (i.e. no one ever documented how any
35 * of the segmentation APIs work), user programs can and do
36 * assume that a struct user_desc that's all zeros except for
37 * entry_number means "no segment at all". This never actually
38 * worked. In fact, up to Linux 3.19, a struct user_desc like
39 * this would create a 16-bit read-write segment with base and
40 * limit both equal to zero.
41 *
42 * That was close enough to "no segment at all" until we
43 * hardened this function to disallow 16-bit TLS segments. Fix
44 * it up by interpreting these zeroed segments the way that they
45 * were almost certainly intended to be interpreted.
46 *
47 * The correct way to ask for "no segment at all" is to specify
48 * a user_desc that satisfies LDT_empty. To keep everything
49 * working, we accept both.
50 *
51 * Note that there's a similar kludge in modify_ldt -- look at
52 * the distinction between modes 1 and 0x11.
53 */
54 if (LDT_empty(info) || LDT_zero(info))
Andy Lutomirski41bdc782014-12-04 16:48:16 -080055 return true;
56
57 /*
58 * espfix is required for 16-bit data segments, but espfix
59 * only works for LDT segments.
60 */
61 if (!info->seg_32bit)
62 return false;
63
Andy Lutomirski0e58af42014-12-04 16:48:17 -080064 /* Only allow data segments in the TLS array. */
65 if (info->contents > 1)
66 return false;
67
68 /*
69 * Non-present segments with DPL 3 present an interesting attack
70 * surface. The kernel should handle such segments correctly,
71 * but TLS is very difficult to protect in a sandbox, so prevent
72 * such segments from being created.
73 *
74 * If userspace needs to remove a TLS entry, it can still delete
75 * it outright.
76 */
77 if (info->seg_not_present)
78 return false;
79
Andy Lutomirski41bdc782014-12-04 16:48:16 -080080 return true;
81}
82
Roland McGrath1bd57182008-01-30 13:31:51 +010083static void set_tls_desc(struct task_struct *p, int idx,
Roland McGrath4c79a2d2008-01-30 13:31:52 +010084 const struct user_desc *info, int n)
Roland McGrath1bd57182008-01-30 13:31:51 +010085{
86 struct thread_struct *t = &p->thread;
87 struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
88 int cpu;
89
90 /*
91 * We must not get preempted while modifying the TLS.
92 */
93 cpu = get_cpu();
94
Roland McGrath4c79a2d2008-01-30 13:31:52 +010095 while (n-- > 0) {
Thomas Gleixner9f5cb6b2017-12-15 20:35:11 +010096 if (LDT_empty(info) || LDT_zero(info))
Thomas Gleixner9a98e772017-08-28 08:47:40 +020097 memset(desc, 0, sizeof(*desc));
Thomas Gleixner9f5cb6b2017-12-15 20:35:11 +010098 else
Roland McGrath4c79a2d2008-01-30 13:31:52 +010099 fill_ldt(desc, info);
100 ++info;
101 ++desc;
102 }
Roland McGrath1bd57182008-01-30 13:31:51 +0100103
104 if (t == &current->thread)
105 load_TLS(t, cpu);
106
107 put_cpu();
108}
109
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110/*
111 * Set a given TLS descriptor:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700112 */
Roland McGrathefd1ca52008-01-30 13:30:46 +0100113int do_set_thread_area(struct task_struct *p, int idx,
114 struct user_desc __user *u_info,
115 int can_allocate)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116{
117 struct user_desc info;
Andy Lutomirskic9867f82016-04-26 12:23:30 -0700118 unsigned short __maybe_unused sel, modified_sel;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
120 if (copy_from_user(&info, u_info, sizeof(info)))
121 return -EFAULT;
122
Andy Lutomirski41bdc782014-12-04 16:48:16 -0800123 if (!tls_desc_okay(&info))
124 return -EINVAL;
125
Roland McGrathefd1ca52008-01-30 13:30:46 +0100126 if (idx == -1)
127 idx = info.entry_number;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700128
129 /*
130 * index -1 means the kernel should try to find and
131 * allocate an empty descriptor:
132 */
Roland McGrathefd1ca52008-01-30 13:30:46 +0100133 if (idx == -1 && can_allocate) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700134 idx = get_free_idx();
135 if (idx < 0)
136 return idx;
137 if (put_user(idx, &u_info->entry_number))
138 return -EFAULT;
139 }
140
141 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
142 return -EINVAL;
143
Roland McGrath4c79a2d2008-01-30 13:31:52 +0100144 set_tls_desc(p, idx, &info, 1);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700145
Andy Lutomirskic9867f82016-04-26 12:23:30 -0700146 /*
147 * If DS, ES, FS, or GS points to the modified segment, forcibly
148 * refresh it. Only needed on x86_64 because x86_32 reloads them
149 * on return to user mode.
150 */
151 modified_sel = (idx << 3) | 3;
152
153 if (p == current) {
154#ifdef CONFIG_X86_64
155 savesegment(ds, sel);
156 if (sel == modified_sel)
157 loadsegment(ds, sel);
158
159 savesegment(es, sel);
160 if (sel == modified_sel)
161 loadsegment(es, sel);
162
163 savesegment(fs, sel);
164 if (sel == modified_sel)
165 loadsegment(fs, sel);
166
167 savesegment(gs, sel);
168 if (sel == modified_sel)
169 load_gs_index(sel);
170#endif
171
172#ifdef CONFIG_X86_32_LAZY_GS
173 savesegment(gs, sel);
174 if (sel == modified_sel)
175 loadsegment(gs, sel);
176#endif
177 } else {
178#ifdef CONFIG_X86_64
179 if (p->thread.fsindex == modified_sel)
180 p->thread.fsbase = info.base_addr;
181
182 if (p->thread.gsindex == modified_sel)
183 p->thread.gsbase = info.base_addr;
184#endif
185 }
186
Linus Torvalds1da177e2005-04-16 15:20:36 -0700187 return 0;
188}
189
Al Viro2cf09662013-01-21 15:25:54 -0500190SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
Roland McGrath13abd0e2008-01-30 13:30:45 +0100191{
Al Viro2cf09662013-01-21 15:25:54 -0500192 return do_set_thread_area(current, -1, u_info, 1);
Roland McGrath13abd0e2008-01-30 13:30:45 +0100193}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700194
195
196/*
197 * Get the current Thread-Local Storage area:
198 */
199
Roland McGrath1bd57182008-01-30 13:31:51 +0100200static void fill_user_desc(struct user_desc *info, int idx,
201 const struct desc_struct *desc)
202
203{
204 memset(info, 0, sizeof(*info));
205 info->entry_number = idx;
206 info->base_addr = get_desc_base(desc);
207 info->limit = get_desc_limit(desc);
208 info->seg_32bit = desc->d;
209 info->contents = desc->type >> 2;
210 info->read_exec_only = !(desc->type & 2);
211 info->limit_in_pages = desc->g;
212 info->seg_not_present = !desc->p;
213 info->useable = desc->avl;
214#ifdef CONFIG_X86_64
215 info->lm = desc->l;
216#endif
217}
Roland McGrath13abd0e2008-01-30 13:30:45 +0100218
Roland McGrathefd1ca52008-01-30 13:30:46 +0100219int do_get_thread_area(struct task_struct *p, int idx,
220 struct user_desc __user *u_info)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700221{
222 struct user_desc info;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700223
Roland McGrathefd1ca52008-01-30 13:30:46 +0100224 if (idx == -1 && get_user(idx, &u_info->entry_number))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700225 return -EFAULT;
Roland McGrath1bd57182008-01-30 13:31:51 +0100226
Linus Torvalds1da177e2005-04-16 15:20:36 -0700227 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
228 return -EINVAL;
229
Roland McGrath1bd57182008-01-30 13:31:51 +0100230 fill_user_desc(&info, idx,
231 &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700232
233 if (copy_to_user(u_info, &info, sizeof(info)))
234 return -EFAULT;
235 return 0;
236}
237
Al Viro2cf09662013-01-21 15:25:54 -0500238SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700239{
Al Viro2cf09662013-01-21 15:25:54 -0500240 return do_get_thread_area(current, -1, u_info);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241}
Roland McGrath4c79a2d2008-01-30 13:31:52 +0100242
243int regset_tls_active(struct task_struct *target,
244 const struct user_regset *regset)
245{
246 struct thread_struct *t = &target->thread;
247 int n = GDT_ENTRY_TLS_ENTRIES;
248 while (n > 0 && desc_empty(&t->tls_array[n - 1]))
249 --n;
250 return n;
251}
252
253int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
254 unsigned int pos, unsigned int count,
255 void *kbuf, void __user *ubuf)
256{
257 const struct desc_struct *tls;
258
Dan Carpenter8f0750f2012-03-24 10:52:50 +0300259 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
Roland McGrath4c79a2d2008-01-30 13:31:52 +0100260 (pos % sizeof(struct user_desc)) != 0 ||
261 (count % sizeof(struct user_desc)) != 0)
262 return -EINVAL;
263
264 pos /= sizeof(struct user_desc);
265 count /= sizeof(struct user_desc);
266
267 tls = &target->thread.tls_array[pos];
268
269 if (kbuf) {
270 struct user_desc *info = kbuf;
271 while (count-- > 0)
272 fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
273 tls++);
274 } else {
275 struct user_desc __user *u_info = ubuf;
276 while (count-- > 0) {
277 struct user_desc info;
278 fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
279 if (__copy_to_user(u_info++, &info, sizeof(info)))
280 return -EFAULT;
281 }
282 }
283
284 return 0;
285}
286
287int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
288 unsigned int pos, unsigned int count,
289 const void *kbuf, const void __user *ubuf)
290{
291 struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
292 const struct user_desc *info;
Andy Lutomirski41bdc782014-12-04 16:48:16 -0800293 int i;
Roland McGrath4c79a2d2008-01-30 13:31:52 +0100294
Dan Carpenter8f0750f2012-03-24 10:52:50 +0300295 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
Roland McGrath4c79a2d2008-01-30 13:31:52 +0100296 (pos % sizeof(struct user_desc)) != 0 ||
297 (count % sizeof(struct user_desc)) != 0)
298 return -EINVAL;
299
300 if (kbuf)
301 info = kbuf;
302 else if (__copy_from_user(infobuf, ubuf, count))
303 return -EFAULT;
304 else
305 info = infobuf;
306
Andy Lutomirski41bdc782014-12-04 16:48:16 -0800307 for (i = 0; i < count / sizeof(struct user_desc); i++)
308 if (!tls_desc_okay(info + i))
309 return -EINVAL;
310
Roland McGrath4c79a2d2008-01-30 13:31:52 +0100311 set_tls_desc(target,
312 GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
313 info, count / sizeof(struct user_desc));
314
315 return 0;
316}